Radiation-emitting semiconductor components based on GaN are disclosed, for example, by U.S. Pat. No. 5,210,051. Such semiconductor components contain a semiconductor body with an active GaN layer that is applied to an SiC substrate. The semiconductor body is contacted on the front on the light-emitting GaN layer and on the back on the SiC substrate.
It is also disclosed by U.S. Pat. No. 5,874,747, for example, how to use related nitrides and ternary or quaternary mixed crystals based on them instead of GaN. Included among them in particular are the compounds AlN, InN, AlGaN, InGaN, INAlN, and AlInGaN.
The term “III-V nitride semiconductor” as used below refers to these ternary and quaternary mixed crystals as well as to gallium nitride itself.
It is also known how to produce GaN semiconductor crystals by epitaxy. A sapphire crystal or SiC is ordinarily used as substrate. According to U.S. Pat. No. 5,928,421, an SiC substrate is preferred with regard to avoiding lattice defects, since GaN layers grown on sapphire have a large number of lattice defects because of the relatively large lattice mismatch between sapphire and GaN.
One drawback of radiation-emitting GaN semiconductor components consists of the fact that at the surface at which the radiation produced in the semiconductor body is emitted, a large refractive index discontinuity occurs at the transition from semiconductor body to the surroundings. A large refractive index discontinuity leads to a considerable fraction of the radiation being reflected back into the semiconductor body and to the radiation yield of the component thereby being reduced.
One cause of this is the total reflection of the radiation produced at the emission surface. Light rays are completely reflected back into the semiconductor body if the angle of incidence of the light rays at the emission surface is greater than the angle of total reflection, each based on the normal to the surface. As the difference between the refractive index of the semiconductor body and that of the surroundings increases, the angle of total reflection decreases and the fraction of totally reflected radiation rises.
Light rays whose angle of incidence is smaller than the angle of total reflection are also partially reflected back into the semiconductor body, with the back-reflected fraction becoming larger as the difference between the refractive indices of the semiconductor body and of the surroundings increases. A large refractive index discontinuity, such as that occurring with GaN components, therefore leads to large reflection losses at the emission surface. The back-reflected radiation is partially absorbed in the semiconductor body or escapes at surfaces other than the emission surface, so that the overall radiation yield is reduced.
One means of increasing the radiation yield consists of applying a reflector to the substrate of the semiconductor body. This is shown, for example, in DE 43 05 296. This again points the radiation back-reflected into the semiconductor body in the direction of the emission surface, so that the back-reflected portion of the radiation is not lost but is at least partially likewise emitted after one or more internal reflections.
In the case of radiation-emitting GaN components pursuant to the state of the art, it is a drawback in this regard to use an absorbing substrate such as SiC, for example. The radiation reflected back into the semiconductor body is absorbed in large part by the substrate, so that it is impossible to increase the radiation yield by means of a reflector.
U.S. Pat. No. 5,786,606 discloses a method for producing radiation-emitting semiconductor components based on GaN in which an SiC layer is first grown by epitaxy on a SIMOX substrate (Separation by IMplantation of OXygen) on an SOI substrate (Silicon On Isolator). A plurality of GaN-based layers are then deposited on the SiC layer.
However, the radiation yield of the component is reduced by the SiC layer, since a portion of the radiation produced is absorbed in the SiC layer. Also, the epitaxial formation of an SiC layer with adequate crystal quality requires a high production cost.
The task underlying this invention is to provide a III-V nitride semiconductor component with increased light yield. It is also the purpose of this invention to develop a method for producing such semiconductor components.
This task is accomplished by a semiconductor component and a production method disclosed herein.
Beneficial refinements of the invention are the objects of various embodiments disclosed herein, including beneficial forms of embodiment of the production process.